Study Predicts Perpetual Drought for Southwest

Apr 01, 2007

Southwestern North America faces a future of long periods of extreme drought resembling the Dust Bowl of the 1930s and the dry years of the 1950s, according to a study.

Researcher said their findings, published on April 5 at the Web site of the journal Science, show that there is a broad consensus among climate models that the transition to a more arid climate probably has already begun.

The conclusions have implications on policies and decision making that may protect the region from such extreme climate conditions, researchers said. "The arid lands of southwestern North America will imminently become even more arid as a result of human-induced climate change just at the time that population growth is increasing demand for water, most of which is still used by agriculture," said Richard Seager, senior research scientist at the Lamont-Doherty Earth Observatory at Columbia University and one of the lead authors of the study. "The West, and in particular, the United States and Mexico, need to plan for this right now, coming up with new, well-informed and fair deals for allocation of declining water resources."

The study involved projections of human-made climate change conducted by 19 different climate-modeling groups around the world using different climate models. According to the researchers, the projections show widespread agreement that southwestern North America -- and the subtropics in general -- are heading toward a climate even more arid than now. The models indicate that human-induced aridification becomes marked early in the current century. In the Southwest, the levels of aridity seen in the 1950s multiyear drought, or the 1930s Dust Bowl, become the new climatology by mid-century: a perpetual drought.

In contrast to historical droughts, future drying is not linked to any particular pattern of change in sea surface temperature but seems to be the result of an overall surface warming driven by rising greenhouse gases. Evidence for this is that subtropical drying occurs in atmosphere models alone when they are subjected to uniform increases in surface temperature, the researchers said. "Our study emphasizes the fact that global warming not only causes water shortage through early snow melt, which leads to significant water shortage in the summer over the Southwest, but it also aggregates the problem by reducing precipitation," said Mingfang Ting, Doherty senior research scientist also at Lamont-Doherty and one of the study's co-authors

The study also shows that in addition to the southwestern North America, other land regions to be hit hard by subtropical drying include southern Europe, North Africa and the Middle East, as well as parts of South America.

The study was conducted in close collaboration with scientists at the National Oceanic & Atmospheric Administration's Geophysical Fluid Dynamics Laboratory.